The double fisherman's bend used to be the preferred knot for joining two ropes to abseil on. It is still popular, but has been somewhat superseded by the one-sided overhand bend due to the fact that it is more prone to catching on sharp edges or in cracks on the pull-down, and is difficult to untie after weighting.
It is strong and so is still the knot of choice for rescue operations, and for joining the two ends of a rope sling.
It can also be used to join the ends of tape together, like the tape knot, but in tape it is almost impossible to untie after it has been weighted.
Some people tie a reef knot in the middle to make it easier to untie. However, this makes the knot even bulkier and more prone to catching on edges.
|Tie a double overhand knot in the first rope, around the second rope, as shown.|
|Then tie another double overhand in the second rope, around the first.|
|Pull tight and set the knot|